ABSTRACT Pebble flow characteristics can be significantly affected by the configuration of pebble bed, especially for HTGR pebble beds. How to achieve a desired uniform flow pattern without stagnation is the top priority for reactor design. Pebbles flows inside some specially designed pebble bed with arc-shaped contraction configurations at the bottom, including both concave-inward and convex-outward shapes are explored based on discrete element method. Flow characteristics including pebble retention, residence-time frequency density, flow uniformity as well as axial velocity are investigated. The results show that the traditionally designed pebble bed with cone-shape bottom is not the most preferred structure with respect to flow pattern for reactor design. By improving the contraction configuration, the flow performance can be significantly enhanced. The flow in the convex-shape configuration featured by uniformity, consistency and less stagnation, is much more desirable for pebble bed design. In contrast, when the shape is from convex-forward to concave-inward, the flow shows more nonuniformity and stagnation in the corner although the average cross-section axial velocity is the largest due to the dominant middle pebbles.

中文翻译：

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3D 收缩对卵石床中卵石流动均匀性和停滞的影响

摘要 卵石床的配置会显着影响卵石流动特性，特别是对于高温气冷堆卵石床。如何在没有停滞的情况下实现所需的均匀流动模式是反应器设计的首要任务。基于离散元方法探索了一些特殊设计的底部具有弧形收缩配置的卵石床内部流动的卵石，包括凹向内和凸向外的形状。研究了流动特性，包括卵石滞留、停留时间频率密度、流动均匀性以及轴向速度。结果表明，就反应器设计的流型而言，传统设计的具有锥形底部的球床不是最优选的结构。通过改进收缩配置，可以显着提高流动性能。具有均匀性、一致性和较少停滞的凸形配置中的流动，更适合球床设计。相比之下，当形状从前凸到内凹时，尽管由于中间卵石占主导地位，平均横截面轴向速度最大，但在拐角处流动显示出更多的不均匀性和停滞。